Technical Field
The present invention relates to a frequency-modulated continuous-wave (FMCW) radar apparatus. In particular, the present invention relates to an FMCW radar device that transmits an electromagnetic wave of which the frequency linearly increases and decreases, receives a returned electromagnetic wave of the transmitted wave that has been reflected by a target, and obtains relative distance and the like of the target from a beat signal based on the received wave and the transmitted wave.
Background Art
In general, in the FMCW radar device, an electromagnetic wave, such a wave in the millimeter-wave region, is transmitted such that the frequency thereof linearly increases and decreases in relation to time, and a returned electromagnetic wave that has been reflected by a target ahead is received. The received wave is mixed with the transmitted wave, and as a result, a signal (beat signal) that has a frequency (beat frequency) proportional to the relative distance of the target is extracted. Fast-Fourier transform (FFT) analysis is performed on the extracted beat signal, the frequency is extracted by peak detection, and the relative distance and the like of the target is calculated from the frequency.
In relation to the foregoing, PTL 1 describes a technique for removing noise (noise components having little fluctuation in frequency and level over time) that is steadily applied to the beat signal in the FMCW radar device.
In this technique, spectral distribution data that has a spectral level that is substantially equal to or greater than a predicted level of a steady regular noise component is stored and held in a memory as initial data. Then, spectral distribution data of a beat signal obtained during transmission and reception of a radio wave is compared with the data in the memory at each unit frequency interval. Of the compared data, the lower spectrum level is set as the spectral level of the steady noise component at the frequency, and the data in the memory is updated thereby. The updated noise data is subtracted from the spectral distribution data of the beat signal, and the noise component is removed. The relative distance of an object is determined from the spectral distribution data of the beat signal from which the noise component has been removed.
PTL 1 JP-A-H07-151852
The above-described method described in PTL 1 is that in which a steadily applied noise component in a beat signal is removed. However, in some cases, the beat signal includes noise that dynamically changes depending on the behavior of a target, unlike the noise component that has little fluctuation in frequency and level over time. In this regard, the circuits of the FMCW radar device are divided into a transmission system (DAC, VCO, amplifier, transmission antenna, and the like), a reception system (reception antenna, mixer, and the like), and a baseband system (amplifier and AD converter), and considered separately. In this case, noise that is generated in the transmission system or the reception system as a result of oscillation in a power supply bias circuit of the FMCW radar device results in the beat signal including noise that dynamically changes depending on the behavior of the target. Such noise generation cannot be detected by the method described in PTL 1.